The end uses of vinyl alcohol polymers have been limited despite excellent strength, adhesive and barrier properties. This limitation is partly due to the fact that unplasticized vinyl alcohol polymers show little or no thermoplasticity before the occurrence of decomposition. Resolution of this problem has been sought through the use of external plasticizers such as ethylene glycol, neopentyl glycol and 2,2,4-trimethyl-1,3-pentanediol. However, the use of external plasticizers presents several disadvantages including increased moisture sensitivity, decreased tensile strength, leaching of the plasticizer and decreased oxygen gas barrier properties.
The internal plasticization of polyvinyl alcohol through the use of comonomers. grafting or post-reacton is known in the art. However, the comonomers normally contain ethyleneoxy groups which possess a high degree of water sensitivity. This water sensitivity leads to loss of oxygen barrier properties as water facilitates the diffusion of oxygen through the polymer matrix.
U.S. Pat. No. 2,290,600 discloses vinyl alcohol copolymers prepared from copolymers of vinyl esters with acrylic or methacrylic esters by converting the vinyl ester part of the copolymer into vinyl alcohol units under conditions whereby the acrylic or methacrylic part is not converted into acrylic or methacrylic acid units. respectively. Polymers containing as little as 3% by weight vinyl alcohol units are substantially tougher than the untreated copolymer or the corresponding 100% acrylic or methacrylic ester polymer. Preferably, the total number of vinyl alcohol units in the polymer is kept below 50% and for most purposes within the range from 20 to 2%.
U.S. Pat. No. 3,689,469 discloses a copolymer consisting essentially of 94 to 98 wt % vinyl alcohol and 2 to 6 wt % methylmethacrylate.
U.S. Pat. No. 4,119,604 discloses a copolymer which is 90 to 98 wt % polymerized vinyl alcohol units and 2 to 10 wt % of polymerized ester units which in monomeric form have the formula ##STR2## wherein A is hydrogen or methyl, A' is hydrogen or --COO--Alkyl, and R is hydrogen or methyl. Alkyl contains 1 to 4 carbons. This vinyl alcohol/unsaturated ester copolymer has a degree of hydrolysis in the range between 95% and 100% and has a viscosity between 10 and 60 cps.
U.S. Pat. No. 2,654,717 disclosed the polymerization of mono-unsaturated vinylic monomers containing at least one oxygen atom linked to carbon atoms (an ether linkage) including for example, monomeric compounds corresponding to the general formula EQU CH.sub.2 =C(R)CO.sub.2 (CH.sub.2 CH.sub.2 O).sub.n R.sup.1
where R is hydrogen or methyl, R.sup.1 is aryl, aralkyl or alkyl group and n is 1 or 2.
U.S. Pat. No. 3,203,918 discloses copolymers of vinyl alcohol and beta-hydroxyalkyl acrylate esters wherein the alkyl group of the beta-hydroxyalkyl acrylate esters may contain from 2 to 4 carbon atoms. The copolymers are prepared by the polymerization and subsequent alcoholysis of copolymers of vinyl acetate and the beta-hydroxyalkyl acrylate esters. Films and coatings of such copolymers are characterized by their ability to remain soft and flexible in the absence of plasticizers.